While I was working on the Act 1 mock-up for Mushroom Hill, I had this idea for Act 2, where, instead of the season changing from spring/summer to autumn like in the original game, the time of day would change instead, from day to night. I really liked the idea, so I decided I would make it into a mock-up after making Act 1, and now, I have finally finished it.
It still has the blue mushrooms from the original game's Act 2, alongside some teal mushrooms, but now, they emit some strong light. Fire-flies have now appeared, fluttering about the stage, with a small light that dims and brightens as they fly. And the stars in the background are a reference to/based on the stars from Starlight Zone.
Also, I would imagine the giant mushrooms would glow brighter when jumped on. And maybe there would be lanterns in the level, that you would have to activate by jumping to, latching onto, and pulling down on a bar below them, in reference to the pulley platforms from the original game. And I would also imagine the music would be a mix of Mushroom Hill Zone (Maybe Act 2 specifically), with a similar feel and tempo to Stickerbush Symphony from Donkey Kong Country 2.

Also, yes, I've heard Mania Plus may have a mechanic similar to this idea for every level, but I had this idea before the trailer for Sonic Mania Plus came out. Besides, I currently refuse to watch the Mania Plus trailer for whatever small spoilers it may contain (I literally consider Ray and Mighty's sprites spoilers, just to give you an idea). why did they have to have the same idea. now everyone's gonna think i ripped off mania plus. wahhhhhhhh

Please give credit to me if any sprites from this, besides Sonic and/or the HUD, are used in anything.